查看更多>>摘要：Permafrost regions of Qilian Mountains in China are rich in gas hydrate resources.Once greenhouse gases in deep frozen layer are released into the atmosphere during hydrate mining,a series of negative consequences occur.This study aims to evaluate the impact of hydrate thermal exploitation on regional permafrost and carbon budgets based on a multi-physical field coupling simulation.The re-sults indicate that the permeability of the frozen soil is anisotropic,and the low permeability frozen lay-er can seal the methane gas in the natural state.Heat injection mining of hydrates causes the continuous melting of permafrost and the escape of methane gas,which transforms the regional permafrost from a carbon sink to a carbon source.A higher injection temperature concentrates the heat and causes uneven melting of the upper frozen layer,which provides a dominant channel for methane gas and results in in-creased methane emissions.However,dense heat injection wells cause more uniform melting of the low-er permafrost layer,and the melting zone does not extend to the upper low permeability formation,which cannot provide advantageous channels for methane gas.Therefore,a reasonable and dense num-ber of heat injection wells can reduce the risk of greenhouse gas emissions during hydrate exploitation.
查看更多>>摘要：Obayied sub-basin provides one-third of the annual natural gas production in the Egyp-tian Western Desert.The origin of the Obayied hydrocarbons are however poorly constrained.In this study,the molecular biomarkers of the Obayied hydrocarbon blend were studied to infer on their ori-gin and generation mechanism.The API values are in the range of(41.3°-53.7°)reflecting post-mature hydrocarbons.The molecular biomarkers suggest a generation of Obayied crude from clay-rich fluvio-deltaic source rocks.Age-and maturity-relevant biomarkers(e.g.,Ts/Tm trisnorhopanes and methyl-phenanthrene indices)reflect a successive expulsion of the Obayied crudes from mature Jurassic rocks(＞1％Ro).Biological markers correlate perfectly with those of the Jurassic Khatatba shale and coal ex-tracts attesting.Additionally,the Obayied gases are wet,thermogenic and have been derived from a mature type Ⅲ kerogen(1.3％Ro-2％Ro).The studied gases display compositional characteristics of mixed coal-and oil-type gases,and were therefore derived via primary cracking of the Khatatba coal as well as secondary cracking of the light liquid crudes.The present study clarifies the controls on the geochemical processes responsible for the accumulation of liquid and gas hydrocarbon mix in the deep as well as shallow inverted rift basins of the north Western Desert,Egypt.
查看更多>>摘要：Nearly 1 100 fissures have formed on the Hebei Plain in China.Within the Yellow River-Qinghe River-Zhanghe River shallow buried paleochannel band on the plain,93 ground fissures con-trolled by paleochannels have developed,of which the Wuyi-Fuping ground fissure is a typical paleochannel-controlled fissure located in Hengshui,Hebei Province,with a total length of 3 km,a dominant strike of NE78°,and nearly upright in the shallow layer.The surface damage observed in this fissure primarily manifests as beaded pits,and its activity shows distinct segmentation characteris-tics.On the trench profiles,the offset distance of shallow layers remains consistently around 20 cm within the depth range of 0 to-3 m.An evident flexure is observed in the strata at depths ranging from-4.5 to-7 m.The drilling profile reveals that there is an absence of dislocations in the deeper strata.Nonetheless,the shallow seismic physical profiles unveil the presence of underlying faults beneath the study area,underscoring the intricate formation process and genesis mechanism of the Wuyi-Fuping ground fissure.Firstly,the formation and evolution of the Qingling River's paleochannel were shaped by the actions of fault blocks and underlying faults.The interplay of the regional stress field,fault block movement,and fault activity played pivotal roles in driving the development of this paleochan-nel.Secondly,the paleochannel exerts a controlling influence on the development location and severity of the fissure.During pumping,the confined aquifer within the paleochannel undergoes water loss and compression,resulting in the formation of a surface subsidence funnel.When the tensile stress surpass-es the soil's tensile strength at the funnel's edge,the soil fractures give rise to a ground fissure.Finally,large amounts of surface water generated by heavy rainfall and irrigation can cause existing hidden ground fissures to rupture,emerge,and expand.This paper provides a heretofore generally unknown example,promotes research on the mechanisms of paleochannel-controlled fissures,and has guiding significance for disaster prevention and reduction in this area.
查看更多>>摘要：More than 5 000 landslides or potential landslides have been triggered in the Three Gorg-es Reservoir(TGR)area since the impoundment in 2003.This study aims at investigating the reservoir-induced landslides spatiotemporal and size distribution and its influence factors in the TGR by taking 790 landslides as statistical samples.The landslides exhibit significant regional and sub-regional spatial differences,and numerous landslides occurred at the initial three impoundment stages and the corre-sponding 2-3 cycles of reservoir operations followed,but the landslide frequency decreased dramatical-ly after 2010 from temporal perspective.The relationship between landslide development and topo-graphical,geological as well as hydrological factors were analyzed qualitatively.The reservoir-induced landslides in TGR area exhibit self-organized criticality and the rollover is nearly 2.5 x 104 m2,which could not be attributed to the missing data but the coupled influences imposed by affecting factors.Both the double Pareto and inverse gamma functions are more suitable than the power-law function to present the landslide size characteristics.In term of the fitting precious,the adaptability of the inverse gamma function is better if the landslide inventories are limited.The research results provide founda-tion for the landslide susceptibility maps and hazard risk assessment.
查看更多>>摘要：In this paper,we present an approach to generating probabilistic hazard maps for earthquake-induced landslides using the Newmark Displacement Model(NDM).This model takes the uncertainties associated with the slope properties(e.g.,soil shear strengths,groundwater table location)into consideration,which is coupled with the hydrological model based on geomorphological,geologi-cal,geotechnical,seismological,and rainfall data.Uncertainties and fluctuations in the input parame-ters of the NDM are considered by treating these quantities as β-PERT distributions through Monte Carlo techniques,which allows probability value of the NDM to be cast into hazard maps.Additionally,incorporating Monte Carlo techniques can avoid using conservative input parameters in a determinis-tic approach to capture these uncertainties.Taking the 2017 Jiuzhaigou Mw 6.5 Earthquake in Sichuan Province,Western China as an example,earthquake-induced landslides probability distribution map is generated with the most appropriate displacement threshold(λ=1 cm).Our results show good perfor-mances for realistic landslide hazard assessment,which can serve as a basis for providing a reference for the prediction of earthquake-induced landslide probability and rapid landslide hazard assessment after a strong earthquake.
查看更多>>摘要：Brittleness is of great significance for evaluating the mechanical properties of the slope rock in reservoir area and revealing the brittle failure mechanism of the rocks.Although a series of def-initions of the brittleness and evaluation methods of brittleness index have been proposed,there is still lack of a widely recognized and remarkable standards in these aspects due to the differences in diage-netic process,depositional environment and mineral composition.The previous methods to quantitive-ly estimate the rock brittleness based on energy balance analysis are summarized,which neglect multi-ple influencing factors of the rock brittleness,such as the weight of pre-peak or post-peak mechanical behaviors on the prediction performance of the brittleness index.Based on the typical curves about stress and strain,the relationships between the brittle failure behaviors and the energy evolutions are comprehensively analyzed,then a new method for assessing the brittleness is proposed.Based on pre-peak brittleness index to represent brittle property at pre-peak stage and post-peak brittleness index to determine brittle characteristic at post-peak stage,a new brittleness index is established by additive synthesis method in consideration of the weight of brittleness indexes before and after peak strength,and either of the two brittleness indexes can be punished or compensated by setting different parame-ter values.The results indicate that the proposed brittleness index can represent the brittle change laws for different rock types when a≤0.5,β ≥ 0.5.When evaluating the brittleness of the slope rock in Three Gorges Reservoir(TGR)area,the results show that the rock brittleness in the slope affects the stability of the slope.Therefore,the novel evaluation method can provide reliable results,and the proposed brit-tleness index considering the energy evolution can be applied to assess the brittle property in the reser-voir bank project.
查看更多>>摘要：Volcanic hazard zoning is an effective way to reduce and mitigate volcanic risks.Due to its frequent magmatic unrest and potential for catastrophic eruption,the Changbaishan-Tianchi Volcano is currently the focus of attention for volcanic disaster prevention in China.This study uses past eruption data obtained from geological surveys and geochronological studies,to construct simulations of tephra fall,pyroclastic flows,lava flows,and lahars.Several widely accepted numerical models were adopted to simulate each hazard at different eruption scales.Hazard zoning was then conducted,producing a com-prehensive hazards map of the Changbaishan-Tianchi Volcano.The map identifies areas of high,medi-um,and low hazard,mostly at 0-15,15-60,60-100 km from the edifice.This work serves as the scientific basis for the authorities and general public in the areas around the Changbaishan-Tianchi Volcano in planning for future response,as well as provides a reference for hazard zoning in other areas potentially affected by volcanic hazards.
查看更多>>摘要：Fast water can cause extraordinary bedload transport.Of the record floods considered here,the Jul.26,2022 urban flash flood on the upper River des Peres,St.Louis,Missouri provides par-ticularly well-constrained data on flow conditions associated with large block movement.Field measure-ments and a detailed lidar survey show that concrete slabs as large as 3.0 × 2.5 × 0.33 m3 were moved from the open channel to reside 215 to 450 m inside a 6.5 m-diameter drainage tunnel,some to become part of a 10-m long imbricated pile.Peak flows of 160 m3/s were recorded at a gauging station located only 1.6 km upstream of the tunnel entrance,which provides a good estimate of 4.2 m/s for the peak flow velocity in the tunnel.Available observational data and a new theoretical analysis show that the ra-dius of large boulders that can be moved by flowing water is directly proportional to the velocity head.
查看更多>>摘要：This study describes the clay mineralogy of the Lower Cretaceous(Barremian)rocks of the Wessex Basin for paleoenvironmental interpretations.Seventy-four samples were subjected to opti-cal microscopy,scanning electron microscopy/energy-dispersive X-ray spectroscopy(SEM/EDS),and quantitative evaluation of minerals by scanning electron microscopy(QEMSCAN®)techniques.The re-sults revealed an illite-dominated sedimentation in most sections of the basin,with kaolinite,chlorite,smectite and glauconite occurring in subordinate quantities.Inferred paleoclimatic conditions from the clay mineral trends indicates a warm and dry climate,with seasonal precipitation.Kaolinite to illite ra-tios indicate that more arid climate conditions were prevalent but brief periods of warm and humid conditions were also present.A strong positive correlation between chlorite and tourmaline indicates that excess chlorite may have been contributed from tourmaline-chlorite-schists in a tourmaline-dominated provenance.SEM confirms that most of the clay minerals are detrital in origin but authi-genic kaolinite is also present as vermiform and mica-replacive kaolinite which formed during early diagenetic modification from flushing meteoric waters in warm humid climates.This study is signifi-cant because it demonstrates the importance of multi-proxy methods for understanding clay minerals within sedimentary basins for interpreting the paleoclimatic conditions of depositional systems.
查看更多>>摘要：The active deforming southeastern margin of the Tibetan Plateau has developed series of fault basins filled with fluvial-lacustrine sediment deposited by drainage systems during every stage of its uplifting,the records of Cenozoic sedimentary sequence and detrital provenance in these basins are often obscure,making the interpretation of the drainage reorganization quite difficult.This research discovered the earliest Late Cenozoic fluvial conglomerate in the Yuanmou Basin,one of the fault ba-sins in SE Tibet,and named the conglomerate as'the Yuanmou Gravel Layer(YMG)'.Clast petrogra-phy,morphology and paleocurrent directions of the YMG indicate that the conglomerate is the remain of a large paleo river traversing through the Yuanmou Basin from north to south.Detrital zircon U-Pb ages can imply the YMG has similar provenance areas with Anning,Dadu and Yalong rivers at age peaks of 175-275,600-1 000,and 2 100-2 700 Ma,but the lack of the age peak of 30-100 Ma from Qiang-tang Block implies that the paleo-river was not yet connected with the Jinsha River during the YMG's accumulation.The fluvial-lacustrine strata with gravel beds containing paleosimian fossils comparable to the YMG were deposited～7-11 Ma,further suggesting that the pre-formed south-flowing river was active during the Late Miocene.
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